15.5 Molecular formula and calculations (Keynotes, lesson planner and mcqs)
Chem·One + MCQs
Keynotes · molecular formula
Molecular formula = n × (Empirical formula) where n = (molecular mass) / (empirical formula mass)
Benzene: EF = CH (mass 13), MM = 78 → n = 6 → MF = C₆H₆
Glucose: EF = CH₂O (mass 30), MM = 180 → n = 6 → MF = C₆H₁₂O₆
Hydrocarbon 85.71% C, MM = 84 → EF = CH₂, n = 6 → MF = C₆H₁₂
Water H₂O, H₂O₂ (MF) vs HO (EF for H₂O₂)
CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂ (25g → 27.75g CaCl₂)
Solutions 15.13 · 15.14
Example 15.13: Benzene EF = CH → EF mass = 13
Molecular mass = 78 → n = 78/13 = 6
∴ Molecular formula = 6 × (CH) = C₆H₆
Example 15.14: Glucose EF = CH₂O → EF mass = 12+2+16 = 30
Molecular mass = 180 → n = 180/30 = 6
∴ Molecular formula = 6 × (CH₂O) = C₆H₁₂O₆
15.15 → 25g limestone + excess HCl produces 27.75 g CaCl₂
35‑minute planner
0–7 min
Keynote recap
8–15 min
Ex.15.13/15.14
16–25 min
Stoichiometry (CaCO₃)
26–35 min
MCQs / activity
35 minutes · mastery pacing
10 MCQs · molecular formula
Click on an option – correct answer highlights green.
Activities
Build C₆H₆ model
Mass ratio race
% carbon puzzle
CO₂ from chalk
EF card game
Empirical lab
85.71% C
unknown
84 g/mol
molar mass
C₆H₁₂ (EF = CH₂, n = 6)
